From Divinity Engine Wiki
- call TriggerRegisterForPlayers((TRIGGERGUID)_Trigger)
Registers the _Trigger for all current player characters, so that that whenever one of them enters or leaves the _Trigger, a CharacterEnteredTrigger resp. CharacterLeftTrigger event will be thrown for this trigger/character combination.
- Event triggers are automatically registered for all characters by the engine and can not be unregistered.
- ProcTriggerRegisterForPlayers ensures that the _Trigger is also registered for characters who become players at a later point (i.e. characters recruited into the party), and unregistered again when player characters are dismissed. Use that procedure rather than the TriggerRegisterForPlayers call directly.